The present invention is related to bit-patterned media, and specifically to read/write heads with read after write capabilities (RAW).
In an effort to continue to increase density associated with magnetic media such as disc drives, traditional “continuous” magnetic media have been replaced with “bit-patterned” media. Unlike traditional continuous magnetic media, in which the magnetic material is uniform, bit-patterned media rely on organizing islands of magnetic material between areas of non-magnetic material. Each island (commonly referred to as “bit-island”) acts as a single grain. The areal density can thereby be increased significantly by reducing the volume of the grain without violating the superparamagnetic limit that constrains the areal density of traditional magnetic media.
Along with their potential to increase areal densities beyond the superparamagnetic limit, bit-patterned media based recording systems present a number of specific problems not previously encountered in conventional magnetic media. In particular, bit-island fabrication errors and write synchronization problems present obstacles to reliable storage using bit-patterned media. In conventional magnetic recording systems, there is no need to synchronize the data with the medium during the write process. For this reason, the data is written using a free running clock and sampling instances are recovered during the read process. However, for bit-patterned media, the locations of the bits to be written are predefined (i.e., the bit islands), and this requires a write clock synchronized to the bit island locations. Any mis-synchronization will lead to deletion or insertion of bits while writing. In particular, the deletion or insertion of a bit while writing (sometimes referred to as “cycle slip”) may result in the loss of all data following the deleted or inserted bit. In addition, fabrication errors can result in individual bit islands that cannot be written to or read from.